Analytical Study of Degradation of CIC Conductor Performance Due to Strand Bending and Buckling

Critical current of cable-in-conduit conductors for ITER TF coils was measured using a pair of short cable-in-conduit conductors, which are electrically connected from each other at the bottom joint. It was found from these test results that the measured critical current was lower than that evaluated from the critical current performance of a single strand. One of the explanations for this phenomenon is a nonuniform current distribution due to local degradation caused by strand buckling. To study the influence on the conductor performance, the author developed a new analysis model for the calculation of bending strain due to buckling and then, combined this with the electrical circuit model, which consists of lumped and distributed circuits for the conductor and upper/bottom joints, respectively. Simulation results show that when local degradation exists, nonuniform current distribution is established. This indicated that conductor performance can be degraded by local degradation such as strand buckling.